The present invention relates generally to the field of crawlspace drying systems for homes and more specifically to a crawlspace system that employs negative air pressure.
There is one consistent problem with almost all crawlspaces, too much moisture, which can cause significant amounts of mold and wood rot. To make matters worse, the results of air sampling show that the same molds in the crawlspace of a home are also found in the interior of the home. When the humidity in a crawlspace rises above 60% relative humidity (RH), conditions are favorable to saturate wood and cause mold to grow. When the moisture content of wood reaches above 16% moisture content (MC) conditions are favorable for mold to grow. When the moisture content of wood elevates between 28% and 35%, wood rot will occur. In the summer time throughout much of the country, the crawlspace moisture content is between 22% and 38% MC. The climate in much of the country during the summer months cause the humidity to be sustained above 60% RH. This moist, stagnant air gets trapped inside of crawlspaces causing favorable conditions for mold growth and wood rot. Further, many times owners of these homes will go to their doctor with an unexplained sickness that they cannot overcome. Today technology has progressed in the medical field to the point that doctors are able to diagnose when patients are sick from mold and mold spores. In the majority of cases, there is no visible mold in the home, until the crawlspace is inspected. In all of these cases, extensive testing has shown that the same molds that are present in the crawlspace are also present inside of the living area of the home. This occurs for two reasons, homes are not built airtight, and all crawlspaces are under positive pressure, meaning that outside air flows into the crawlspace and then filters into the living area of the home. When air from the crawlspace filters into the home, mold spores are carried with the air. The contaminated air is pushed into the home through openings in the floor such as, plumbing holes, wiring holes, and seams in flooring.
A typical crawlspace has over 50,000 mold spores per cubic meter of air. Safe levels for breathable air are well below 1000 mold spores per cubic meter of air. Depending on the type of mold, even levels below 1000 mold spores per cubic meter of air can be harmful. Generally speaking, the molds that grow from saturated wood are harmful, and they include stachybotryis, and aspergillus/penicillium. To properly remediate a crawlspace with moderate mold damage is very labor intensive and costly, typically $15,000.00 to $20,000.00 to remediate a crawlspace on a 2400 SF home. Once the remediation is complete, a drying system must still be installed or the crawlspace will need to be remediated again within two years. Homeowners and restoration companies have recently made lawmakers aware of this problem and some states have implemented codes that require a crawlspace ventilation system in all new homes.
According to the EPA, “the most effective way to improve indoor air quality is to eliminate or control sources of pollution, or to reduce their emissions. Another important approach that goes hand in hand with controlling pollution is using mechanical ventilation to lower the concentrations of pollutants in your home by increasing the amount of outdoor air coming inside. Good ventilation is important because it protects both your health and your home. Good ventilation protects you and your family from unpleasant odors, irritating pollutants, and potentially dangerous gases. Well-planned ventilation also helps prevent the growth of mold and mildew, which can cause allergic reactions and aggravate lung diseases such as asthma. Too much moisture in a home can lead to mold, mildew, and other biological growth. This in turn can lead to a variety of health effects ranging from more common allergic reactions, asthma attacks, and hypersensitivity pneumonitis, to death. Excess moisture can be in the form of high relative humidity, leaks in the roof, walls, or plumbing, air moving from the inside or the outside into the walls, or from the basement or crawlspace. Methods to control moisture include fixing any water leaks; providing ventilation in the home; air-sealing; properly using vapor barriers in wall construction, roofs; and preventing soil moisture from entering the home through basements and crawlspaces.”
The Institute of Inspection Cleaning and Restoration states, “Even high humidity or warm moist air condensing on cool surfaces can trigger mold problems. Create negative pressure to prevent mold from spreading.”
Advance Energy addresses the mold problem as follows: “These symptoms are most often noticed in the humid spring and summer seasons but can occur at any time of the year. Often, the heating and air conditioning contractor is the first person the residents call to deal with the problem. Typically though, the problem is not due to a failure of the air conditioning system; it results from poor moisture control in the crawl space.”
For many decades, building codes and conventional wisdom have prescribed ventilation with outside air as the primary method of moisture control in crawl spaces. In the humid Southeast, however, ventilation with outside air only makes moisture problems worse. Recent research by Advanced Energy and others indicates that a new type of crawl space system, with NO vents to the outside, can provide greatly improved moisture control and significant energy savings when properly installed. Unfortunately, there is no cost effective system currently available to deal with this problem. What is currently available in the industry is a mix of high priced equipment that comes with an even higher maintenance price. Crawlspace dehumidifiers are expensive, one 60 pint crawlspace dehumidifier, capable of dehumidifying about 5,000 cubic ft of air, cost approximately $3,000.00 to install. Crawlspace dehumidifiers have many problems. The sealing process of the crawlspace must be very precise, meaning very time consuming. Any crack or hole in the crawlspace after the sealing process allows outside air in, and results in the dehumidifier trying to dry an endless supply of humid air, which of course, it cannot. Further, a dehumidifier will only reduce the humidity 15 to 20 percent and they do not work properly in temperatures above 90° Fahrenheit. If the outside humidity is over 80% RH, crawlspace dehumidifiers are ineffective at reducing the humidity to a safe level. Moreover, reducing the humidity in the air will not dry previously moist wood and insulation. High static airflow is needed to pull the moisture out that has wicked into materials such as wood and insulation. When high airflow moves over the surface of a porous material, it creates pressure or a draft and pulls the moisture out of the material. Wood is not very porous therefore is absorbs moisture slowly and also evaporates moisture slowly making it even more difficult to dry. To make matters worse, the exhaust of a dehumidifier will create more positive pressure in a crawlspace enabling more contaminated air to enter the living space of the home. Each dehumidifier runs on about 9 to 13 Amps and generates heat, meaning they are not very cost effective in energy consumption. Dehumidifiers also have a high break down rate because of the conditions in which they operate.
A more involved crawlspace drying system is a sealing and dehumidifying process that involves covering over the foundation walls with a heavy duty plastic material and installing a dehumidifier. The cost can be between $8,000 and $20,000. This system requires that the mold in the crawlspace be remediated before installation. The cost for mold remediation can be between $8,000.00 and $25,000. In addition, because of the construction of a crawlspace (the tight working area, ducting and wiring that covers up portions of moldy wood) it is very difficult and near impossible to fully remediate a crawlspace of mold. Moreover, the heat and positive pressure generated by the dehumidifier creates a bad environment under the home. The crawlspace air is forced into the home and creates an unsound environment and additional heat inside of the home. Any spores, dust, dirt particles and other particulate in a crawlspace environment will also be forced into the living area.
Another prior system involves hanging twenty to twenty-five 150 CFM fans from the rafters of the crawlspace. There is no price range of this system due to the fact it is not on the market however, due to the amount of hardware involved the price is expected to be high, along with the energy consumption. The problems with this system include, the system is untested and hot damp air is brought into the crawlspace from the outside. Further, the system's low CFM air movement will not have the capability to pull moisture out of wood.
There is another system that pulls air from the attic and sends it down into the crawlspace. Problems of this system include the following: the fan blowing into the crawlspace creates positive pressure in the crawlspace; there is not enough air movement to pull moisture out of wood; attic air is very hot and humid, typical relative humidity is around 20% higher than that outside; and, hot air forced under the home rises and enters the home along with contaminated air.
Yet another system involves installing larger foundation vents, fans and exhaust fans. The cost for an average home is around $2,000 to $5,000. Problems with this system include the crawlspaces may remain under positive pressure, hot humid outside air is brought into the crawlspace, and on rainy and humid days moisture content will actually increase in the crawlspace. Further, the equipment is visible from the outside and must be installed into the foundation, which involves cutting through brick and/or solid block.
What is needed in the field is a cost effective crawlspace system that dries the crawlspace and prevents contaminated, moldy air in the crawlspace from moving into the home. The ideal system would create high enough air movements that will pull out moisture that has wicked into wood and insulation. The ideal system would also create negative air in the crawlspace thereby eliminating harmful contaminated air from entering the home and creating healthy air exchanges in the living area of the home with fresh air from the outside.